Police are trying to identify a man who hit another person in the head with a kerosene container on a San Francisco Municipal Railway light-rail vehicle in the city’s Bayview District on Friday afternoon, police said.

In the biggest study of its kind, researchers at Boston University analyzed the brains of deceased athletes and veterans (all of who had history of repeated head trauma), and found more than 80 percent had signs of CTE, or Traumatic Brain Encephalopathy.